Determining the concentration of an analyte or a marker of physical condition in a biological sample has been an important technique in the field of diagnostics. Markers that have diagnostic value include nutrients, metabolites, enzymes, immunity entities, hormones, and pathogens. The physical characteristics of a biological sample, such as temperature, optical properties, density, and hardness, are also of interest because they can provide indications with diagnostic value. Most determination methods currently in use to detect markers and analytes and many imaging methods employ signal-enhancing agents
Current standard blood analysis (laboratory assay) is performed using blood samples obtained from a subject and assays are generally based on the identification of measurable features of the blood that are used to indicate the presence of a specific known species within the blood. In some instances the measurable features of the blood can be used to calculate the concentration of the known species in the blood. The presence of the species, or its concentration in the blood, is then used as an indicator or a marker and correlated to a certain state of health within an individual. Limitations of this approach of blood analysis include difficulties limitations are the long time needed to perform the various assays (in vivo and ex vivo) resulting in a historical snapshot of blood species as an indicator for dynamic and possibly rapid changing health states, and the reliance upon discrete, known species as adequate markers for health states within an individual.
Much interest has been expressed recently in developing spectroscopic, in particular visible, infrared (IR) or near-infrared (NIR) spectroscopic, techniques to non-invasively or minimally invasively determine blood or tissue chemistry or to analyze blood samples isolated from the patient. These non-invasive techniques have the advantage of eliminating or greatly reducing the need for collection of a blood sample or series of blood samples from a patient, which, in turn avoids the discomfort and complications that can be associated with blood collection. In techniques developed to date, the spectroscopic measurements are used to specifically identify or quantitate a particular marker or analyte, or combination thereof. For example, U.S. patent application Ser. No. 11/091,396 (Publication No. 2005/0222502) discloses a respiratory monitoring apparatus that detects changes in physiological parameters relevant to respiration using near infrared spectroscopy. Similarly, U.S. patent application Ser. No. 11/125,107 (Publication No. 2005/0202567) discloses a spectroscopic assay arrangement and technique for detection of the presence and/or concentration of an analyte in a sample of bodily fluid.
A number of patents and patent applications disclose spectroscopic methods and devices for non-invasive measurement of blood or tissue analytes (See, e.g., U.S. patent application Ser. No. 10/971,447 (Publication No. 2005/0107676), U.S. patent application Ser. No. 10/943,737 (Publication No. 2005/0075546), International PCT Application No. WO 01/016577, International PCT Application No. WO 99/043255, International PCT Application No. WO 93/016629 and U.S. Pat. No. 6,928,311). In each case, the techniques are used to specifically identify or quantitate a specific analyte or characteristic.
There remains a need, therefore, for a reliable, convenient method that permits measurement of the spectral properties of bodily fluid or tissue as an indicator of clinical condition, without the need to use the spectroscopic data to first identify and quantitate a specific analyte or characteristic, which is, in turn, used to extrapolate a clinical condition.
This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.